Sudden cardiac arrest (CA) is one of the leading causes of death worldwide. Despite advances in cardiopulmonary resuscitation (CPR) methods, 60-80% of these arrests result in immediate death, and of the remaining, only about 5 percent are successfully resuscitated to the extent that they are returned to productive lives. The poor outcomes of patients, who initially achieve return of spontaneous circulation (ROSC) after CA are attributed to the post-CA syndrome. While therapeutic hypothermia (TH) has proven effective in clinical studies, no pharmacological agent is available to improve outcome from CA. A protective role for nitric oxide (NO) in ischemia and reperfusion (IR) injury has been suggested by a number of studies. Although originally developed as a selective pulmonary vasodilator, inhaled NO has been shown to have systemic effects in a variety of pre-clinical and clinical studies without causing systemic vasodilation. In preliminary studies that serve as the foundation of this research proposal, we found that breathing a low concentration of NO starting 1h after successful CPR for 23h markedly improves short-term (up to 10 days) neurological and cardiac outcomes and survival in mice after 7.5 min of CA followed by CPR. Of note, the salutary effect of inhaled NO on 10-day survival after CA/CPR was abolished in mice deficient in soluble guanylate cyclase (sGC), a NO receptor. Based on these exciting new observations, we hypothesize that breathing NO after successful CPR from CA improves long-term outcome via sGC-dependent signaling mechanisms. To address this hypothesis, we propose to determine the impact of NO inhalation on the long-term outcome (up to 4 weeks) after CA/CPR (Aim 1), to examine the role of sGC in the protective effects of inhaled NO on outcomes of CA/CPR (Aim 2), and to elucidate the cellular mechanisms responsible for the protective effects of inhaled NO on the long-term outcomes after CA/CPR (Aim 3). Because inhaled NO does not cause systemic hypotension, in contrast to systemic NO-donors, it is uniquely suited for the treatment of post-CA patients in whom blood pressure is often unstable. Successful completion of the proposed studies in small mammals would provide the mechanisms foundation for large animal studies examining the effects of inhaled NO in CA/CPR. Given the established safety profile of inhaled NO, we believe the proposed studies will enable rapid translation of this novel and non- invasive therapeutic strategy to improve outcomes in patients suffering from sudden CA and the post-CA syndrome.